This invention relates to a method and a device for connecting in a liquid-tight manner electric cables connected to electrical devices adapted to operate within the housing of hydraulic machinery, and electric cables connected to controllers disposed outside of a housing at a cable lead-out portion in the housing. The invention also relates to prevention of fluid leakage from the inside to the outside of the housing through the cables and the instrusion of foreign matters, such as water, from the outside into the inside of the housing.
In hydraulically controlled machinery in a hydraulic system, electrical devices are often operated while immersed in a hydraulic fluid. In a hydraulic control system of an automatic transmission, for instance, a solenoid valve is immersed in the hydraulic fluid and is adapted to operate under control of an electronic controller located outside the housing of the hydraulic control system so as to control the shift valve and other components of the hydraulic control system by maintaining the pressure of the hydraulic fluid in the shift valve and other components, or by reducing the pressure by draining the hydraulic fluid.
Electric cables coated with polytetrafluoroethylene, which is designated as Teflon (trade name), referred to hereinafter as Teflon cables, are used for transmitting command signals to such electrical devices which operate while immersed in a hydraulic fluid, because the temperature of the hydraulic fluid often rises to a very high temperature during operation of the hydraulic control system. This coating material, Teflon, has excellent heat-resisting and oil-resisting properties and Teflon cables are durable for extended service in the hydraulic fluid. However, Teflon cables are extremely expensive as compared with ordinary rubber-coated, synthetic rubber-coated or polyethylene-coated electric cables, referred to hereinafter simply as polyethylene cables.
Further, since a Teflon cable or a polyethylene cable is formed by closely coating many intertwisted copper wires with a tubular coating layer, the Teflon cable and the polyethylene cable have a drawback in that hydraulic fluid leaks outside of the housing along the interior of the cable through gaps between the cable coating and the copper wires and through gaps between the component copper wires due to capillarity. This occurs even if a perfectly liquid-tight sealing is provided between the opening of the lead-out portion of the housing and the cable, when a single cable connected at one end thereof to an electrical device disposed within the housing, is passed through the opening and is connected at the other end thereof to a controller.
What is needed is a device for connecting electric cables in a hydraulic system which provides a leak-tight connection under adverse conditions of temperature and exposure and is economical in construction.